View Full Version : "Observable universe" vs actual universe

m1omg

2012-Aug-16, 10:51 PM

Why do so many people think observable universe is the whole universe? I see people making claims like "A googol is SO LARGE that it is even larger than the number of elementary particles in the universe" and they always cite the "observable universe" figures to make it seem "universe is really small in fact". There is a very real possibility that the universe might be in fact be infinite (meaning an infinite number of elementary particles so not even Graham's number might actually approach the actual number of particles in the universe anymore than a googol or the number 1 does) and even the accepted cosmology finite universe models generally predict an universe larger than any human idea of infinity - http://en.wikipedia.org/wiki/Orders_of_magnitude_%28length%29#Astronomical - the lowest boundary for the size of the universe is 250 billion years and the figure predicted by inflational models is more than 10 to the power of a googolplex - in fact that means that the universe is large enough to have a near-infinite number of cosmological horizons that are exactly the same as ours!

If the latter number is correct, the size of the entire universe is much, much, much higher compared to the observable universe than the size of the observable universe compared to a planck volume.

So no, our universe is not just 93 billion light years big (or 14 billion as some people not understanding comoving distance or the expansion of the universe believe). Our universe is probably so big that it contains a near infinite number of your identical twin, doing the exact same thing as you are doing right now. Now that is humbling.

primummobile

2012-Aug-16, 11:09 PM

Just to nitpick... there is no such thing as "near infinite". Either it is infinite or it is not.

m1omg

2012-Aug-16, 11:22 PM

I know that, I used the word near-infinite in the layman context, because the actual possible size of the universe mentioned on Wikipedia and in this paper http://arxiv.org/abs/hep-th/0610199 is larger than any human beings idea of infinity. In short, if this is true, and if you said that the actual universe is as large compared to the observable universe as the observable universe is compared to a single Planck volume, you'd be underestimating the size of the universe by more than a factor of googolplex.

What is even more humbling is that if the resolution proposed in the paper is true, the number mentioned is a lower bound. The universe might just as well be still finite, but unimaginably larger than that or infinite.

grapes

2012-Aug-17, 08:51 AM

Although I don't have a problem with "near-infinite" (it's just any number that's a million times bigger than any number in the current discussion :) ), I have another nit. Just because there are an infinite number of things, it's not necessarily even true that two have to be identical, or even nearly identical. Just saying.

m1omg

2012-Aug-17, 09:12 AM

I'm not saying the entire universe is observable universe repeated infinitely, just that laws of probability say that after a mind bogglingly huge distance (mentioned on that wikipedia page), you are certain to encounter an exact copy of our observable universe. Considering how small any observable universe is compared to the probable size of the actual universe it is like having many identical-color sand grains at the bottom of the Mariana Trench - most of the universe will be very different to our observable universe (in terms of exact structures, there will obviously be stars, galaxies... just like in ours and the same physical laws), but some tiny areas will happen to be exactly like our observable universe because the universe is so big that it can happen out of random chance.

There is an exact number of how far would you have to go before encountering a twin of our observable universe on that Wiki page, with references. It is mind bogglingly big, but much smaller than the "predicted size of the actual universe after inflation" number.

Btw for me "near infinite" is pretty much any number that is so big that it stops mattering in which unit you give it. 10 to the power of 10 to the power of 10 to the power of 122 (sorry, not sure how to insert superscripts) is such a big number that you could say that the predicted size of the universe is 10 to the power of 10 to the power of 10 to the power of 122 Planck lenghts and it wouldn't matter. Plack lenghts, light years, gigaparsecs, lenghts of the observable universe ... any unit stops being meaningful at this scale.

Selfsim

2012-Aug-17, 10:02 AM

I have another nit. Just because there are an infinite number of things, it's not necessarily even true that two have to be identical, or even nearly identical. Just saying.In an infinite universe which has existed for an infinite amount of time, there will be an exact doppelganger (duplicate) of oneself .. as everything that is possible, will happen (like an exact duplicate) ... and has already happened an infinite number of times !

I believe Max Tegmark, (theoretical physicist), produced these, and several other remarkable theoretical ramifications, in a paper several years ago .. (Mind you, there's a very long trail of deep theoretical thinkers who have trodden this same path before him ...)

Interestingly also, its the only theoretical paradigm, (I'm aware of), in which 'other' life can be legitimately predicted to exist with 100% certainty ...

Pity its not practically possible to show that such an infinite universe actually exists beyond our observable one, however ...

:)

Neat thread ! .. Thanks m1omg !

Cheers

Strange

2012-Aug-17, 12:15 PM

In an infinite universe which has existed for an infinite amount of time, there will be an exact doppelganger (duplicate) of oneself .. as everything that is possible, will happen (like an exact duplicate) ... and has already happened an infinite number of times !

I just can't buy that. There are an infinite number of integers. None of them are the same. This is like the often repeated claim that (all versions of) the complete works of Shakespeare must appear in the decimal expansion of Pi. It ain't necessarily so.

Incidentally, looking up some data for a similar discussion elsewhere, I came across this:

If the universe is finite but unbounded, it is also possible that the universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies, formed by light that has circumnavigated the universe.

http://en.wikipedia.org/wiki/Observable_universe

primummobile

2012-Aug-17, 12:40 PM

I just can't buy that. There are an infinite number of integers. None of them are the same. This is like the often repeated claim that (all versions of) the complete works of Shakespeare must appear in the decimal expansion of Pi. It ain't necessarily so.

Incidentally, looking up some data for a similar discussion elsewhere, I came across this:

http://en.wikipedia.org/wiki/Observable_universe

I disagree with that. What do you mean that there are an infinite number of integers? The infinite set contains every finite set. You are a finite set of quantum states. To be otherwise your body would need to be made up of an infinte number of particles, which is obviously nonsense.

If you have infinitely repeating series of finite states you must have infinite copies of those states. In a random system they are likely to be pretty far removed from one another spatially, especially when you increase the number of variables. If our solar system started as one of a gazillion possible quantum states that are available with a gajillion elementary particles then that state will be repeated somewhere in an infinite sequence.

Strange

2012-Aug-17, 02:47 PM

I disagree with that. What do you mean that there are an infinite number of integers?

The cardinality (size) of the set of natural numbers (or integers) is infinity. No two integers in that set are the same.

If you have infinitely repeating series of finite states you must have infinite copies of those states.

But you can have an infinite non-repeating series (made up of finite states) as well. Just because it is infinite doesn't mean it has to be repeating.

Moose

2012-Aug-17, 03:38 PM

The cardinality (size) of the set of natural numbers (or integers) is infinity. No two integers in that set are the same.

He's right. {1, 2, 2, 2, 5} is a valid subset of integers.

Your statement "no two integers in that set are the same" would be accurately written as "no two unique integers in that set are the same". Tautological, yes. Listing them in numerical order, and uniquely, is just a convention. Not a property of integers. Otherwise, the concept of identity would fail utterly.

Any identity that equals 1, (2/2, for example), is a representation of an integer, and falls within the integer set.

That said, the properties of the set of integers says absolutely nothing about the properties of the universe. While such a metaphor can be useful to explain an assertion, it does nothing whatsoever to support it. The only answer we really have to the size and shape of the actual universe is "we don't know; we may never know; and that won't stop us from guessing".

[Edit: Actually, you know what? Never mind. I don't think I can let myself get involved in this discussion. This is going to wind me up far too much, and it's just not important enough to offset the hassle of setting off my OCD today. Enjoy.]

primummobile

2012-Aug-17, 03:47 PM

The cardinality (size) of the set of natural numbers (or integers) is infinity. No two integers in that set are the same.

Ok, that was a really stupid question for me to ask. For some reason, and I have no idea why now, I was thinking that you were referring to digits and not numbers. Please forget I ever asked that.

But you can have an infinite non-repeating series (made up of finite states) as well. Just because it is infinite doesn't mean it has to be repeating.

I'm not so sure about that. Just to keep it simple and not make my calculator crap out on me, let's just consider a sequence of ten digits where you can only use each digit one time. There are 3,628,000 (10!) possible ways for those digits to be arranged. Somewhere in the value of pi you should expect to see each of those possible arrangements, and you should be able to find each arrangement an infinite number of times. But, that's not a realistic comparison to the universe because the digits can be repeated in each sequence. In that case, the number of possible ten digit combinations is 10^10, which is 10,000,000,000. That is significantly larger, but in an infinite sequence every grouping of ten digits must be one of those 10 billion combinations. That means you should expect to find each of those sequences an infinite number of times. Of course there are further complications, especially when you consider that the 10 digit sequence can begin and end in random places. I don't know how that would change the possibilities, but it would make it much, much larger. But if you try it an infinite number of times you will find the same patterns repeating in there somewhere.

Have you ever read anything about those people who attempt to make predictions based on the Bible or other large books? They are able to find all kinds of names and almost anything else just by selecting random characters from the text and looking for a pattern. The results are hokum, but imagine if the book were infinite. You'd be able to find anything in there.

Strange

2012-Aug-17, 05:57 PM

Ok, that was a really stupid question for me to ask.

I did wonder :)

Please forget I ever asked that.

Asked what?

I'm not so sure about that. Just to keep it simple and not make my calculator crap out on me, let's just consider a sequence of ten digits where you can only use each digit one time. There are 3,628,000 (10!) possible ways for those digits to be arranged.

But your "each digit one time" introduces a constraint that may not always be valid. Take the first 10 digits of the decimal expansion of pi and it doesn't apply (1415926535), although it gets closer to being true over longer sequences. But Pi is only guaranteed to contain every possible sequence (an infinite number of times) if it is normal. Which it almost certainly is but it isn't known. It is possible that at some point in the decimal expansion the digit 3, say, no longer occurs.

Strange

2012-Aug-17, 06:00 PM

While such a metaphor can be useful to explain an assertion, it does nothing whatsoever to support it. The only answer we really have to the size and shape of the actual universe is "we don't know; we may never know; and that won't stop us from guessing".

Agreed. And, just to be clear, I am not asserting that the universe is or is not infinite, or that if it is infinite that it does or doesn't repeat itself. I'm only saying that it might or might not. We don't (can't?) know.

[Edit: Actually, you know what? Never mind. I don't think I can let myself get involved in this discussion. This is going to wind me up far too much, and it's just not important enough to offset the hassle of setting off my OCD today. Enjoy.]

I feel similarly!

primummobile

2012-Aug-17, 06:25 PM

But your "each digit one time" introduces a constraint that may not always be valid. Take the first 10 digits of the decimal expansion of pi and it doesn't apply (1415926535), although it gets closer to being true over longer sequences. But Pi is only guaranteed to contain every possible sequence (an infinite number of times) if it is normal. Which it almost certainly is but it isn't known. It is possible that at some point in the decimal expansion the digit 3, say, no longer occurs.

I don't argue that. I was just showing a progression from 'each digit once' to random.

I just personally believe that if the possible conditions are finite and you have infinite iterations you will stumble across infinite copies of each possible condition. But I argued this in another thread for too long, and not very long ago. I'm content to let it be as well.

m1omg

2012-Aug-17, 07:23 PM

It is technically possible that universe is smaller than the observable universe, but extremely unlikely. A flat universe suggests an infinite universe and so far WMAP indicates that the universe is flat or near-flat, meaning that it is either infinite or finite but extremely big. Furthermore the 250 billion light year limit is, quoting Wikipedia "lower bound of the (possibly infinite) radius of the universe, if it is a 3-sphere, according to one estimate using the WMAP data at 95% confidence[23]. It equivalently implies that there are at minimum 21 particle horizon-sized volumes in the universe.".

In short, it is very unlikely that our universe is a small one, and most likely, it is either an unthinkably large one or infinite one.

About numbers being an infinite set yet not repeating... true, but structures in the universe are not numbers. Numbers follow after each other, subatomic particles, planets, people, aliens... do not. The laws of probability and quantum mechanics don't apply to integers but they apply to the physical universe. You can have a mathematical construct where nothing ever repeats, but not physical things.

m1omg

2012-Aug-17, 07:28 PM

In an infinite universe which has existed for an infinite amount of time, there will be an exact doppelganger (duplicate) of oneself .. as everything that is possible, will happen (like an exact duplicate) ... and has already happened an infinite number of times !

I believe Max Tegmark, (theoretical physicist), produced these, and several other remarkable theoretical ramifications, in a paper several years ago .. (Mind you, there's a very long trail of deep theoretical thinkers who have trodden this same path before him ...)

Interestingly also, its the only theoretical paradigm, (I'm aware of), in which 'other' life can be legitimately predicted to exist with 100% certainty ...

Pity its not practically possible to show that such an infinite universe actually exists beyond our observable one, however ...

:)

Neat thread ! .. Thanks m1omg !

Cheers

Thanks for all the responses folks, it is a very interesting topic to think about

The neat thing is, the universe does not even have to be infinite for that (the predicted distance between dopplergangers is mind bogglingly huge, but much, much lower than the size of the universe according to cosmological inflation). And it can be proven by the geometry of the universe - if universe is curved inwards, it is finite, if it is flat or saddle shaped, it is infinite http://en.wikipedia.org/wiki/Shape_of_the_universe .

Strange

2012-Aug-17, 07:51 PM

You can have a mathematical construct where nothing ever repeats, but not physical things.

Penrose tiles?

primummobile

2012-Aug-17, 08:36 PM

Thanks for all the responses folks, it is a very interesting topic to think about

The neat thing is, the universe does not even have to be infinite for that (the predicted distance between dopplergangers is mind bogglingly huge, but much, much lower than the size of the universe according to cosmological inflation). And it can be proven by the geometry of the universe - if universe is curved inwards, it is finite, if it is flat or saddle shaped, it is infinite http://en.wikipedia.org/wiki/Shape_of_the_universe .

The number I've heard, and remembered, is 10^43,000,000,000,000 LY between duplicates on average.

m1omg

2012-Aug-17, 08:46 PM

The number I've heard, and remembered, is 10^43,000,000,000,000 LY between duplicates on average.

Indeed, and the lenght between dopplergangers of our exact observable universe is predicted to be 10^10^115 light years. This is a number large enough that if you said the lenght is 10^10^115 Planck lenghts it would not be a big mistake. It pales however to the lower limit on the size of the universe predicted by some inflational models which is 10^10^10^122 light years. In short, the distance predicted between dopplergangers of both single people and entire observable universes is huge enough to surpass any number human mind can imagine, but there is probably enough space in the universe for more than a googolplex "observable universe dopplergangers".

That is, if the universe is really big, but finite. If it is infinite, then the number of dopplergangers will be infinity.

primummobile

2012-Aug-17, 08:58 PM

That is, if the universe is really big, but finite. If it is infinite, then the number of dopplergangers will be infinity.

Yup. I agree with that.

primummobile

2012-Aug-17, 09:01 PM

Penrose tiles?

My wife wants to put Penrose tiling in the basement and I am resisting vigorously.

m1omg

2012-Aug-17, 09:04 PM

Penrose tiles are interesting, but then, they are specifically designed to not repeat, unlike the universe.

primummobile

2012-Aug-17, 09:17 PM

Penrose tiles are interesting, but then, they are specifically designed to not repeat, unlike the universe.

The way I understand Penrose tiles is that they are non-symmetrical but any finite pattern in the tiles will eventually repeat itself as you add to it. I may be wrong about that. If I am, then it's not Penrose tiling that my wife wants to put into the basement.

m1omg

2012-Aug-17, 09:51 PM

The way I understand Penrose tiles is that they are non-symmetrical but any finite pattern in the tiles will eventually repeat itself as you add to it. I may be wrong about that. If I am, then it's not Penrose tiling that my wife wants to put into the basement.

That is the way I understood it too. I suspect that whatever "non repeating" qualities Penrose tiling has it probably doesn't apply to a group of Penrose tilings a googolplex meters wide.

Selfsim

2012-Aug-17, 10:36 PM

The neat thing is, the universe does not even have to be infinite for that (the predicted distance between dopplergangers is mind bogglingly huge, but much, much lower than the size of the universe according to cosmological inflation). And it can be proven by the geometry of the universe - if universe is curved inwards, it is finite, if it is flat or saddle shaped, it is infinite http://en.wikipedia.org/wiki/Shape_of_the_universe .Hi m1omg;

I'm intrigued

When you say: "the universe does not even have to be infinite for that" I'm left with some ambiguity about exactly what you mean. Could you, perhaps, clarify a little for me ?

At the moment, I think I'm still justified in sticking with the concept that in the practical universe we live in, our measurements will always be bounded by practical observational horizons (eg: the cosmological horizon), and our measurements will always have uncertainties, which become an issue when making estimates of such huge distances/timescales and geometries
so, we will always be bounded by these 'practicality horizons'. In theory however, such horizons might be irrelevant, so at least in theory, I get that doppelgangers are certain. But in practice they, (and inevitability, other lifeforms) are not.

I think the distinction of: 'in theory' and 'in practice' are very important in preserving clarity in these kinds of discussions, and in this particular case, the theory is constantly under test
and the tests are asymptotically limited by measurement resolutions, and uncertainties.

Regards

m1omg

2012-Aug-17, 11:09 PM

The only real rule that must be met is that the universe has the same physical laws everywhere as here. This is supported by both the Big Bang theory and the inflation theories, plus it was confirmed that the structure of the universe is homongenous at any scale beyond http://en.wikipedia.org/wiki/Observable_universe#End_of_Greatness http://en.wikipedia.org/wiki/Cosmological_Principle . In short, universe produces galaxies, planets, superclusters everywhere and there is no magical "life giving" property of this exact region of space. The existence of dopplergangers is reality in any universe large enough, not just theory. And the universe does not have to be infinite simply because the odds of multiple exact Jonases or Earths or Hubble volumes are not infinitely small, just very very low so the distance between dopplergangers can be accurately calculated.

I don't think this really has anything to do with the "other life" issue, as the probability for alien life within this Hubble volume is unimaginably larger than the probability of a dopplerganger appearing, which is why the distance between dopplerganger is extremely large.

So either universe is smaller than 10^43000000000000 light years, or each of us has a dopplerganger. It all sounds very silly until you learn to appreciate the magnitude of numbers like this. You live in a ridiculously huge universe, you get ridiculously improbable things happening.

It is the same as with winning a lottery million years in a row, normally it is impossible, but if you played the lottery for a let's say 10^100 years, it starts not just being possible but a necessary logical result of playing the lottery that long. The only difference is that playing the lottery for 10^100 years is impossible while the universe being roomy enough for dopplergangers is a very serious possibility because of cosmic inflation and the geometry of the universe.

Cougar

2012-Aug-18, 01:44 AM

It all sounds very silly until you learn to appreciate the magnitude of numbers like this.

This reminds me of a story Murray Gell-Mann told in The Quark and the Jaguar. As a student, he was assigned to calculate the probability that a human on Earth would suddenly appear on the moon, due to quantum tunneling. The result is also an extremely low probability. IIRC, he took that as so ridiculously small, it might as well be zero, and was so for all practical purposes.

I abhor infinity. :razz:

DoggerDan

2012-Aug-18, 09:20 AM

Our universe is probably so big that it contains a near infinite number of your identical twin, doing the exact same thing as you are doing right now. Now that is humbling.

I just did something fairly unpredictable. I slapped myself. You're saying that if the universe is indeed infinite that there's a duplicate me out there somewhere with precisely the same molecules including those in my hand which just slapped my face?

Isn't it equally likely, statistically speaking, that there is infinite variation such that no two people would ever be exactly alike?

HenrikOlsen

2012-Aug-18, 09:25 AM

In an infinite universe which has existed for an infinite amount of time, there will be an exact doppelganger (duplicate) of oneself .. as everything that is possible, will happen (like an exact duplicate) ... and has already happened an infinite number of times !

I just can't buy that. There are an infinite number of integers. None of them are the same.

The chance of any specific integer being picked by random out of all integers is infinitesimally small, the chance of an integer less than a given integer being picked is also infinitesimally small, individual integers don't have a finite non-zero chance of happening so the argument doesn't apply to them.

This is like the often repeated claim that (all versions of) the complete works of Shakespeare must appear in the decimal expansion of Pi. It ain't necessarily so.

Pi isn't random, arguments about random numbers doesn't apply to its digits.

primummobile

2012-Aug-18, 01:09 PM

This reminds me of a story Murray Gell-Mann told in The Quark and the Jaguar. As a student, he was assigned to calculate the probability that a human on Earth would suddenly appear on the moon, due to quantum tunneling. The result is also an extremely low probability. IIRC, he took that as so ridiculously small, it might as well be zero, and was so for all practical purposes.

I abhor infinity. :razz:

I know what you mean about infinity. It seems to create more problems than it solves.

When I was in college, there was always a little bit of a competition between the math professors and the engineering professors. The engineers thought the mathematicians had their heads in the clouds, and the mathematicians thought the engineers were too grounded.

Anyway, I remember being in one of my introductory electrical theory classes and there being a student arguing with the instructor about how capacitor theory has to be wrong because a capacitor never really fully charges or discharges, although we usually consider them to be after five or six time constants. So the professor illustrated his point with a story...

Two men, a mathematician and an engineer, were placed against the wall on one side of a room. A bucket of gold was placed on the far wall. They were told that they could have the gold if they followed one simple rule. In walking to the gold, they were only allowed to cover half the distance to the far wall with each step. The mathematician threw up his hands and walked out of the room because he knew that no matter what he did he could never cover that distance to the far wall. The engineer, on the other hand, just walked across the room until he was close enough to reach out and grab the gold with his hand.

I don't know why, but I've always gotten a little bit of a kick out of that story. I think it's a good illustration of the difference between theory and reality.

primummobile

2012-Aug-18, 01:12 PM

I just did something fairly unpredictable. I slapped myself. You're saying that if the universe is indeed infinite that there's a duplicate me out there somewhere with precisely the same molecules including those in my hand which just slapped my face?

Isn't it equally likely, statistically speaking, that there is infinite variation such that no two people would ever be exactly alike?

Not really. There aren't an infinite number of things you could do. There would be infinite copies of you who slapped their face, and infinite almost-copies of you who did not. While the number of things you could do is really beyond our comprehension, it is still finite and therefore contained an infinite number of times in the infinite set.

dapifo

2012-Aug-18, 06:56 PM

So either universe is smaller than 10^43000000000000 light years, or each of us has a dopplerganger. It all sounds very silly until you learn to appreciate the magnitude of numbers like this. You live in a ridiculously huge universe, you get ridiculously improbable things happening.

When you are talking about the dinension of the observable universe,,,you only are considering the positive dimensions: 10^n (where n>0 and near infinite)...but why you dont consider also the universes that could be in the negative dimensions (where n<0 and also possibly near infinite)?

There are the same possibility of having things, bodies and entities....into a very small dimensions...possibly near 10^-(10^100) meters !!!

Hornblower

2012-Aug-18, 08:11 PM

When you are talking about the dinension of the observable universe,,,you only are considering the positive dimensions: 10^n (where n>0 and near infinite)...but why you dont consider also the universes that could be in the negative dimensions (where n<0 and also possibly near infinite)?

There are the same possibility of having things, bodies and entities....into a very small dimensions...possibly near 10^-(10^100) meters !!!

Can you show us, in appropriate mathematical detail, why you think the probability of such a system is the same?

primummobile

2012-Aug-18, 08:31 PM

When you are talking about the dinension of the observable universe,,,you only are considering the positive dimensions: 10^n (where n>0 and near infinite)...but why you dont consider also the universes that could be in the negative dimensions (where n<0 and also possibly near infinite)?

There are the same possibility of having things, bodies and entities....into a very small dimensions...possibly near 10^-(10^100) meters !!!

Are you implying that if we had the right equipment we could see little people running around and galaxies forming at scales several times smaller than the Planck Length? That's so off the wall that I don't even know what to say to it. How do you back this up?

dapifo

2012-Aug-18, 10:51 PM

Can you show us, in appropriate mathematical detail, why you think the probability of such a system is the same?

Can you show us, in appropriate mathematical detail, why you think that not is similar?

The only difference is due our brain structure...it is easyer to imagine large things...till infinite...than smaler things....that we think they to need have a limit (??)...but why?..it is only a problem of our brain strunture...

You are talking as something possible (but silly) that "the universe is smaller than 10^43000000000000 light years, or each of us has a dopplerganger"...but you cannot shape and accept an universe smaller than Planck dimension....(???)

dapifo

2012-Aug-18, 10:58 PM

Are you implying that if we had the right equipment we could see little people running around and galaxies forming at scales several times smaller than the Planck Length? That's so off the wall that I don't even know what to say to it. How do you back this up?

I donīt think that we could see little people running around and galaxies forming,, as well we know now...but yes I think that is possible that other type of beings and entities could be there....Why do you see it so different that they exist at larger dimensions of 10^43000000000000 light years....and that could exist dopplerganger?

primummobile

2012-Aug-18, 11:33 PM

Because there is a limit to how small subatomic particles can be. Once you get so small there's nothing smaller to break it up into. There's nothing limiting how large of a space we live in and it's pretty easy to prove mathematically that in infinite iterations you will have infinite duplication. Something infinitely small is completely different and you need to back up what you said without attacking the argument and saying "if you can make it big you can make it small." That's not a case for what you are implying.

dapifo

2012-Aug-19, 02:32 AM

Because there is a limit to how small subatomic particles can be. Once you get so small there's nothing smaller to break it up into.

How can you ensure so categorically this?

You could say that "according to current theories ...", but always that in science somebody have made such categorical statements ... they have always ended up being false ... remember the meaning of atom ...Now Plack (and streams) seams to be the smallest dimension....(???)

Do you really think that there is a limit for smallest particles?

dapifo

2012-Aug-19, 10:41 AM

Why do so many people think observable universe is the whole universe? [...] the accepted cosmology finite universe models generally predict an universe larger than any human idea of infinity - http://en.wikipedia.org/wiki/Orders_of_magnitude_%28length%29#Astronomical - the lowest boundary for the size of the universe is 250 billion years and the figure predicted by inflational models is more than 10 to the power of a googolplex [...] If the latter number is correct, the size of the entire universe is much, much, much higher compared to the observable universe than the size of the observable universe compared to a planck volume. [...] So no, our universe is not just 93 billion light years big (or 14 billion as some people not understanding comoving distance or the expansion of the universe believe).

Please, could you tell me which there is the "most" possible dimension that current (mainstream) physics forsee for the Whole Universe?

I supose that the Observable Universe is a sphere of 13.700 millions light years of radius.(??)

Our universe is probably so big that it contains a near infinite number of your identical twin, doing the exact same thing as you are doing right now. Now that is humbling.

Although that probabilistically it could be possible .... this is nothing more than a meaningless fallacy...because you donīt take into account the Time :

- The Time that this dopplergangers will exist....do they coexist in the same time?

- And If the succession of events will be the same ... and for how long....(1 second?... 10.000 milliosn of years?)

You only onsider an instant picture !!!!

Hornblower

2012-Aug-19, 11:49 AM

Can you show us, in appropriate mathematical detail, why you think that not is similar?The only difference is due our brain structure...it is easyer to imagine large things...till infinite...than smaler things....that we think they to need have a limit (??)...but why?..it is only a problem of our brain strunture...

You are talking as something possible (but silly) that "the universe is smaller than 10^43000000000000 light years, or each of us has a dopplerganger"...but you cannot shape and accept an universe smaller than Planck dimension....(???)

My bold. No I cannot, and since I did not assert anything one way or the other I see no need to attempt any such thing. All I did was ask a question.

If I did wish to make such an analysis, I would need to learn the math and physics behind the best theory we have to date and then compare it step by step with an alternative scenario.

dapifo

2012-Aug-19, 12:02 PM

If I did wish to make such an analysis, I would need to learn the math and physics behind the best theory we have to date and then compare it step by step with an alternative scenario.

OK..but first you have to take into account (consider) this possibility.... If you donīt accept this possibility ...then you will never need (wish) to make such an analysis, and you would never need to learn the math and physics behind the best theory we have to date and then compare it step by step with an alternative scenario.

Hornblower

2012-Aug-19, 12:18 PM

OK..but first you have to take into account (consider) this possibility.... If you donīt accept this possibility ...then you will never need (wish) to make such an analysis, and you would never need to learn the math and physics behind the best theory we have to date and then compare it step by step with an alternative scenario.

For me it is not a matter of accepting or rejecting. I simply do not care. Perhaps a future unification of general relativity and quantum mechanics could enable discoveries that would make me change my mind.

Swift

2012-Aug-19, 12:41 PM

I don't know why this thread was started in OTB. I'm not sure what exactly is the theme of this thread, and it seems to be rapidly turning into ATM. Rather than trying to sort out who is claiming what and dropping the various pieces into ATM, it is just closed. Anyone wants to further discuss this, start your own threads in an appropriate forum.

And dapifo, your posts here seem a lot like your recently closed thread in S&T on dimensions. If you wish to discuss your ideas on this any further, you need to start a thread in ATM.

Swift

2012-Aug-20, 03:13 PM

After some discussion among the moderation team, we have decided to move this thread to Astronomy (from OTB) and reopen it.

There are speculative aspects to this topic, and that is fine. But advocacy of non-mainstream ideas will not be tolerated. Questions and speculation are fine, advocacy is not.

dapifo, if you discuss your "scale" ideas, or any other non-mainstream views in this thread again, you will be severely infracted and suspended; you will get no further warnings.

dapifo

2012-Aug-21, 12:24 PM

Why do so many people think observable universe is the whole universe? I see people making claims like "A googol is SO LARGE that it is even larger than the number of elementary particles in the universe" and they always cite the "observable universe" figures to make it seem "universe is really small in fact". There is a very real possibility that the universe might be in fact be infinite (meaning an infinite number of elementary particles so not even Graham's number might actually approach the actual number of particles in the universe anymore than a googol or the number 1 does) and even the accepted cosmology finite universe models generally predict an universe larger than any human idea of infinity - http://en.wikipedia.org/wiki/Orders_of_magnitude_%28length%29#Astronomical - the lowest boundary for the size of the universe is 250 billion years and the figure predicted by inflational models is more than 10 to the power of a googolplex - in fact that means that the universe is large enough to have a near-infinite number of cosmological horizons that are exactly the same as ours!

If the latter number is correct, the size of the entire universe is much, much, much higher compared to the observable universe than the size of the observable universe compared to a planck volume.

So no, our universe is not just 93 billion light years big (or 14 billion as some people not understanding comoving distance or the expansion of the universe believe). Our universe is probably so big that it contains a near infinite number of your identical twin, doing the exact same thing as you are doing right now. Now that is humbling.

If the universe began in a Big Bang 13.7 billion years ago, and as you and some theories say is big enough to "contains a near infinite number of your identical twin" .... 10 ^ 10 ^ 115 ym .... Then my questios is:

Which is the speed of the expansion of the Universe inflation? ... This must be huge! ... nearly infinite!

Strange

2012-Aug-21, 12:51 PM

Which is the speed of the expansion of the Universe inflation? ... This must be huge! ... nearly infinite!

Expansion isn't measured as a speed. It is a "rate", a rate of change of scale; e.g. how long it would take for the distance between two point to increase by 10%. And if you think about that, that is what makes apparent speed proportional to distance.

So, equivalently, it can be measured as how velocity increases with distance. It is measured as about 74 (km/s)/Mpc. In other words, for every million parsecs of distance from the observer, the rate of expansion increases by about 74 kilometers per second. So it is actually quite small. but noticeable because the universe is really, really big.

Note that there is also a hypothetical early period (inflation) when the rate of expansion was much, much greater.

dapifo

2012-Aug-21, 01:12 PM

Then...13.7 billions years x 74 km/s = 13.700.000.000 x 365 x 24 x 60 x 60 x 74 km= (13.7x365x24x36x74) 10^11 = 2*10^19 km = 2* 10 ^22 meters?

Cougar

2012-Aug-21, 01:29 PM

Then...13.7 billions years x 74 km/s = 13.700.000.000 x 365 x 24 x 60 x 60 x 74 km= (13.7x365x24x36x74) 10^11 = 2*10^19 km = 2* 10 ^22 meters?

If that's the answer, what's the question?

Actually, you left out the "per megaparsec" part. The expansion rate between any two objects is dependent on the distance between them. If that distance is 1 Mpc, the rate is 74 km/sec. If the distance is 2 Mpc, the rate of expansion between them is 2x74 km/sec or 148 km/sec. Etc.

dapifo

2012-Aug-21, 03:41 PM

If that's the answer, what's the question?

Actually, you left out the "per megaparsec" part. The expansion rate between any two objects is dependent on the distance between them. If that distance is 1 Mpc, the rate is 74 km/sec. If the distance is 2 Mpc, the rate of expansion between them is 2x74 km/sec or 148 km/sec. Etc.

OK..OK..The question was ...

If the universe began in a Big Bang 13.7 billion years ago, and as you and some theories say is big enough to "contains a near infinite number of your identical twin" .... 10 ^ 10 ^ 115 ym .... Then my questios is:

Which is the speed of the expansion of the Universe inflation? ... This must be huge! ... nearly infinite!

Strange

2012-Aug-21, 03:48 PM

OK..OK..The question was ...

If the universe began in a Big Bang 13.7 billion years ago, and as you and some theories say is big enough to "contains a near infinite number of your identical twin" .... 10 ^ 10 ^ 115 ym .... Then my questios is:

Which is the speed of the expansion of the Universe inflation? ... This must be huge! ... nearly infinite!

And ... hasn't that been answered?

dapifo

2012-Aug-21, 04:05 PM

And ... hasn't that been answered?

OK yes...but it is not clear because :

1 pc = 3*10^16 m.....1Mpc = 3*10^22 m....near the obserable universe....then the universe in increasing very few.

And also at begeaning of Big-bang....slower.

How do yo spect that now the Universe could be larger than 10 ^ 10 ^ 115 ym ?????

Strange

2012-Aug-21, 04:29 PM

The observable universe is currently, I believe, about 46 billion light years in radius; i.e. the stuff that emitted light 13.7bn years ago is now 46bn ly away.

As pointed out at the start of the thread, the whole universe may be be much bigger than that (or even infinite).

Note that even at the current rate of expansion there are objects with an apparent velocity away from us much greater than the speed of light. If the universe is large enough, that has always been true (because relative velocity is proportional to distance).

dapifo

2012-Aug-21, 08:06 PM

When you say Observable Universe...do you reffer to the part of the Whole Universe that we can see and detect?...Wny do you say that "the stuff that emitted light 13.7bn years ago is now 46bn ly away."?

When you say that Whole Universe may be be much bigger than that (or even infinite)...do you reffer to the Universe started in the Big-bang....or you include other space and Universes?

Strange

2012-Aug-21, 08:09 PM

When you say Observable Universe...do you reffer to the part of the Whole Universe that we can see and detect?...Wny do you say that "the stuff that emitted light 13.7bn years ago is now 46bn ly away."?

Because it has moved that far in the last 13.7 bn years.

Wasn't all this covered in the very first post in this thread.

dapifo

2012-Aug-21, 09:10 PM

Why do so many people think observable universe is the whole universe? I see people making claims like "A googol is SO LARGE that it is even larger than the number of elementary particles in the universe" and they always cite the "observable universe" figures to make it seem "universe is really small in fact". There is a very real possibility that the universe might be in fact be infinite (meaning an infinite number of elementary particles so not even Graham's number might actually approach the actual number of particles in the universe anymore than a googol or the number 1 does) and even the accepted cosmology finite universe models generally predict an universe larger than any human idea of infinity - http://en.wikipedia.org/wiki/Orders_of_magnitude_%28length%29#Astronomical - the lowest boundary for the size of the universe is 250 billion years and the figure predicted by inflational models is more than 10 to the power of a googolplex - in fact that means that the universe is large enough to have a near-infinite number of cosmological horizons that are exactly the same as ours!

If the latter number is correct, the size of the entire universe is much, much, much higher compared to the observable universe than the size of the observable universe compared to a planck volume.

So no, our universe is not just 93 billion light years big (or 14 billion as some people not understanding comoving distance or the expansion of the universe believe). Our universe is probably so big that it contains a near infinite number of your identical twin, doing the exact same thing as you are doing right now. Now that is humbling.

Please, uniffy the terms...You talk abbout; Whole Universe (=) Actual Universe, Our Universe (=) Observable Universe,...

Then Our Universe (=) Observable Universe seams to be 93 billion light years big(?)= aprox. 10^26 meters

And the Whole Universe (=) Actual Universe could be near infinite or larger than 10^10 ^115 LY (?) ...or the Whole universe's size is at least 10^23 times larger than the size of the observable universe.... then 10^23 * 93 * 10^9 LY= 10^(23+11+15) meters = aprox. 10^60 meters

SkepticJ

2012-Aug-21, 11:32 PM

The observable universe is currently, I believe, about 46 billion light years in radius; i.e. the stuff that emitted light 13.7bn years ago is now 46bn ly away.

As pointed out at the start of the thread, the whole universe may be be much bigger than that (or even infinite).

Note that even at the current rate of expansion there are objects with an apparent velocity away from us much greater than the speed of light. If the universe is large enough, that has always been true (because relative velocity is proportional to distance).

Wait a minute, how old is the whole universe?

Is it the same age as the observable universe, or older? If older, and if the universe is infinite, is it infinitely old? Is the observable universe like a fairly new, growing fat cell in an immortal and ever expanding morbidly obese person?

Strange

2012-Aug-21, 11:36 PM

Wait a minute, how old is the whole universe?

Good question. I don't know. I think it is generally assumed to be the same as the observable universe. But I'm not sure we can ever answer your questions.

dapifo

2012-Aug-22, 12:30 AM

Good question. I don't know. I think it is generally assumed to be the same as the observable universe. But I'm not sure we can ever answer your questions.

OK...OK..Now I understand how whole universe could so large..if it older than observable....

Strange

2012-Aug-22, 11:08 AM

OK...OK..Now I understand how whole universe could so large..if it older than observable....

Well, it doesn't have to be. I'm not sure why you think it needs to be older to be any particular size? If it is bigger than the observable universe, then I assume it must have always been (roughly) that much bigger than the part that became the observable universe. To take one extreme, if the universe iss infinitely large, then it must have always been infinitely large.

dapifo

2012-Aug-22, 06:53 PM

Well, it doesn't have to be. I'm not sure why you think it needs to be older to be any particular size? If it is bigger than the observable universe, then I assume it must have always been (roughly) that much bigger than the part that became the observable universe. To take one extreme, if the universe iss infinitely large, then it must have always been infinitely large.

During all the thread I was assuming that the Whole Universe starts also in the Big-bang 13,7 billions years ago....then I didnīt understand how it could expand so much (till near infinite).

Now I realize that you accept that is possible that Our Universe started in the Big-bang 13,7 billions years ago....inside other older and larger Whole Universe (!!!)

That is what I have been deffending always ... !!!... and now I understand about the m1omg phrase: "Our universe is probably so big that it contains a near infinite number of your identical twin, doing the exact same thing as you are doing right now.".....That there will be so many (near infinites) bubbles like Our Universe..that it is probabilistically possible that one could exact to Our Universe.

Strange

2012-Aug-22, 07:06 PM

During all the thread I was assuming that the Whole Universe starts also in the Big-bang 13,7 billions years ago....then I didnīt understand how it could expand so much (till near infinite).

I don't see why not; doesn't it just depend how big it was to start with?

Now I realize that you accept that is possible that Our Universe started in the Big-bang 13,7 billions years ago....inside other older and larger Whole Universe

That is possible, but I don't think it is the generally accepted model. It sounds like a version of the "eternal inflation" model: http://en.wikipedia.org/wiki/Eternal_inflation

and now I understand about the m1omg phrase: "Our universe is probably so big that it contains a near infinite number of your identical twin, doing the exact same thing as you are doing right now.".....That there will be so many (near infinites) bubbles like Our Universe..that it is probabilistically possible that one could exact to Our Universe.

I don't think that is what he meant; I assumed he meant within the (one) universe.

Currently we don't have any evidence for multiple big bangs, bubble universe, anything existing before the big bang, etc. So any ideas are pretty much speculative at the moment.

dapifo

2012-Aug-22, 07:51 PM

[...] if you said that the actual universe is as large compared to the observable universe as the observable universe is compared to a single Planck volume, you'd be underestimating the size of the universe by more than a factor of googolplex.[...]

Planck Dimension= 10^-35 meter

Observable Universe = 10^+26 meters = 10^60 Planck Dimension

If actual universe is as large compared to the observable universe as the observable universe is compared to a single Planck volume, then:

actual universe = 10^95 meters....near Googol meters....not Googolplex (!!!)

If actual universe = 1 Googolplex meters= 10^(10^100) meters...then will be = near 10^(10^98) times Our Observable Universe (!!!)

Shaula

2012-Aug-22, 09:43 PM

And if the universe is actually carried on the backs of turtles 10^700 metres across then the universe is 10^674 times larger than our observed universe.

I don't get why you are just spraying out random numbers here. Why should the universe care about base 10?

Reality Check

2012-Aug-22, 11:08 PM

During all the thread I was assuming that the Whole Universe starts also in the Big-bang 13,7 billions years ago....then I didnīt understand how it could expand so much (till near infinite).

This is one of the things that people tend not to get about the Big Bang - it was not an explosion as we experience in everyday life. The universe did not expand into anything to get bigger.

Frequently Asked Questions in Cosmology: What is the Universe expanding into (http://www.astro.ucla.edu/~wright/cosmology_faq.html#XIN)?

It was an expansion in spacetime which did not change the size of the universe. The universe is usually considered be infinitely big (no limits to its size).

What is changing are distances within the universe.

dapifo

2012-Aug-22, 11:13 PM

And if the universe is actually carried on the backs of turtles 10^700 metres across then the universe is 10^674 times larger than our observed universe.

I don't get why you are just spraying out random numbers here. Why should the universe care about base 10?

m1omg did...

dapifo

2012-Aug-22, 11:19 PM

It was an expansion in spacetime which did not change the size of the universe. The universe is usually considered be infinitely big (no limits to its size).What is changing are distances within the universe.

That , if it is true, is new for me!!!...It is very interesting !!!

Then the universe allready exist before the Big-bang... with the same size than now.....and the only change "after the Big-bang" were the distances within the universe (!!!??)

I donīt understand....!!!

Reality Check

2012-Aug-23, 12:03 AM

Then the universe allready exist before the Big-bang... with the same size than now.....and the only change "after the Big-bang" were the distances within the universe (!!!??)

Or maybe the universe did not exist before the Big Bang.

Or maybe the universe had a different "size" before the Big Bang.

All we know is that there was a Big Bang and that the universe did not change its size. It stays as infinite if it is infinite. It stays as finite if finite.

Shaula

2012-Aug-23, 05:12 AM

The Big Bang theory only states that the observable universe grew from a hot dense state finite time ago. It says very little about the wider universe, it says very little about the state of the observable universe before the point in time where the model breaks down.

m1omg did...

He mentioned some bounds from inflationary models. That is all they are. You just seemed to be making up numbers and linking them with "if then if then if" statements.

dapifo

2012-Aug-23, 05:10 PM

All we know is that there was a Big Bang and that the universe did not change its size. It stays as infinite if it is infinite. It stays as finite if finite.

That is accepted by mainstream?

Shaula

2012-Aug-23, 06:26 PM

That is accepted by mainstream?

Not really. Because as I said ... We do not know. There is a cut-off beyond which we just don't know. Go back far enough and we do not know. Statements that we do are based on what could be faulty extrapolations beyond the point at which we have a working theory.

noncryptic

2012-Sep-14, 09:25 AM

Arguments against exact duplicates in an infinite universe;

"Exact duplicate" involves not only the state of an object at a particular moment in time, but would involve the history of the object.

The history of an object is in part determined by its surroundings. So for there to be exact duplicates there must be exact duplicates of entire regions of the universe, with the exact same history. In fact it must be a pattern of repeating duplicate regions such that the effect that those regions have on one another is identical.

Additional argument: an infinite universe contains an infinite amount of matter/energy, which allows for infinite variation of the composition of objects. So an infinite universe does not inevitably lead to duplicate objects.

Cougar

2012-Sep-16, 03:48 PM

It was an expansion in spacetime which did not change the size of the universe.

Your wording seems to be a bit misleading. It is normally said that it was an expansion OF spacetime, not in spacetime. And of course the "size" of the universe is getting bigger. If it's expanding, how could it not be getting bigger? An infinite universe (unknown to be the case) does not mean it has any particular size. It means, AFAIK, as time goes on, whatever size it is increases without end. The amount of baryonic and dark matter in the universe is apparently finite. No more of this stuff is appearing within the universe. As space continues to expand, the density of matter continues to decrease. This would seem to argue against "exact duplicates" in some distant region of the universe. Even if the "whole universe" is 1023 times larger than the portion that is visible to us, as Alan Guth originally estimated, that is nowhere near the size required to run into a duplicate of our galaxy, which, per Tegmark, is more like 101028 meters from here.

Reality Check

2012-Sep-17, 12:26 AM

Your wording seems to be a bit misleading. It is normally said that it was an expansion OF spacetime, not in spacetime.

Thanks for the correction.

And of course the "size" of the universe is getting bigger. If it's expanding, how could it not be getting bigger?

Not really. You are thinking about an expansion IN spacetime, e.g an explosion.

Infinity is the concept of being without bounds. Think about a set of numbers that is infinite:

What happens if you add a another item to the set? It is still infinite.

What happens if you add an infinite number of items to the set? It is still infinite.

Basically if you treat infinity as a number then it has strange properties, e.g. add 1 and it is still infinity , multiple by infinity and it is still infinity.

See Hilbert's paradox of the Grand Hotel (http://en.wikipedia.org/wiki/Hilbert%27s_paradox_of_the_Grand_Hotel).

So an infinite universe that is expanding still is infinite, i.e. its "size" does not change.

You have more space and so the density of matter decreases.

Reality Check

2012-Sep-17, 12:28 AM

That is accepted by mainstream?

Yes: If infinite then the size of the universe remains as infinite. If finite then the size of the universe remains as finite (but increasing AFAIK).

Cougar

2012-Sep-17, 12:16 PM

What happens if you add a another item to the set? It is still infinite.

I hate infinity. :)

publiusr

2012-Sep-22, 07:53 PM

Not really. There aren't an infinite number of things you could do. There would be infinite copies of you who slapped their face, and infinite almost-copies of you who did not.

Q tells me all my other selves are just as broke as me.

We can't win.

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